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Homework Help: Someone help!

  1. Oct 17, 2004 #1
    OK this problem is probably really easy, but I totally have no idea how to handle it. Please help! Here goes:

    A 20kg cart on wheels has been pushed up against a wall with a spring (k= 244N/m) between the cart and the wall. If the spring is compressed a distance of 0.1m and a force of 20N is continued to be applied toward the wall, what will the acceleration of the object be?
  2. jcsd
  3. Oct 17, 2004 #2
    You know mass, you know k, you know dx, you know F.

    F = -kx = 1/2kx^2 = ma

    a = -kx/m
  4. Oct 17, 2004 #3
    One question: how come kx is negative?
  5. Oct 17, 2004 #4
    it is usually opposite to the direction of inertia
  6. Oct 17, 2004 #5
    OK thanks for the help!
  7. Oct 18, 2004 #6

    Doc Al

    User Avatar

    Staff: Mentor

    To find the acceleration of an object, use Newton's 2nd law. First find the net force on the cart. There are two (horizontal) forces on the cart: the spring, pushing out from the wall; and the applied force of 20 N pushing towards the wall. Find the net force and then calculate the acceleration [itex]a = F_{net}/m[/itex].

    The force law for springs: F = -kx, tells you the force that the spring exerts for a given stretch or compression x (from equilibrium). The negative sign means that the force is in the opposite direction of the compression. For example: If the spring is pushed in, the force it exerts pushes out.
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